(a) Field of the Invention
The present invention concerns processes for heating a thermic enclosure by means of at least one burner which produces at least two flames.
(b) Description of Prior Art
In the case of combustions which are produced from a combustible material and a fuel material consisting of air, it is easy to develop many forms of flames which are adapted to the designs of thermic enclosures in which different processes of heating are carried out. The mass flows which are used during combustions with air (about 1400 kg/MW) and the quantities of movement which may result therefrom enable to relatively easily shape the flames to give appropriate forms thereto, for example filiform or in the form of balls. When flames with high thermic performances are desired, the utilization of highly preheated air (between 1200.degree. and 1400.degree. C.) is necessary and the above mentioned ease of operation considerably decreases for technological reasons.
A very large number of combustion applications requiring high thermic performances imply the use of oxygen, as fuel material in specific industrial burners. The mass flows being different (about 300 kg/MW with oxygen), the burners utilizing pure oxygen as fuel material do not actually enable to control the problems of shaping of the flames and even less the zoning of the combustion products enabling to reduce the risks of oxidation of the materials under treatment.
On the other hand, with respect to the production of polluting materials, such as nitrogen oxides (NOx) the usual techniques of recirculation and shaping of the combustible and/or fuel material are not without disadvantage on the thermic processes. As a matter of fact, recirculation consists in producing zones close to the nose of the burner where the already already burnt gases are returned into the flame. The result is a decrease of the local concentrations of oxygen and a substantial decrease of the temperature of the flame which enable to minimize the quantities of nitrous oxides, the decrease of the flame temperature being on the other hand detrimental to the heat efficiency of the heating process. Also, the combustion in stages enables to carry out a combustion under sub-stoichiometric condition in a first zone close to the nose of the burner, the additional combustible or fuel material being brought in by means of a third injection which is later on mixed with the gas issued from the first combustion zone. This technique also promotes the minimization of the production of oxides of carbon but considerably modifies the thermic efficiency of the heating process.